NC programs, which are generated using an NC programming system, are often made up of a sequence of points. Connecting these points by linear segments produces polylines. The execution of such an NC program in a machine tool may produce undesirably sharp changes in direction between the linear segments. These may be caused by, among other things, numerical inaccuracies in the generation of a path in the NC programming system. Sharp changes in direction, however, may result in an unnecessary loss of time, since their generation may require a reduction in the feed rate so as not to exceed any dynamic limit values of the machine axes. Moreover, troublesome irregularities may be produced on the workpiece surface in the process.
Hence, it may be desirable to smoothen such polylines prior to further processing in a numerical control.
Thus, German Published Patent Application No. 43 03 090 describes a method for generating reference variables for position control loops in numerically controlled machines, in which from sequences of path setpoint values, position setpoint values are generated by filtering and weighting, which are fed to the position control loop as reference variables. Filtering and weighting attenuates sharp changes in direction contained in the path setpoint values.
A disadvantage of a method of this type may be that the effectiveness of the attenuation depends on the feed rate of the machine tool. Thus, at a high feed rate, a strong attenuation is to be expected, while a slow feed rate results in weaker attenuation.
German Published Patent Application No. 44 30 003 describes a method in which data records made up of points describing a polyline are already smoothed before being transferred to the machine tool control. For smoothing the polyline, a plurality of consecutive points are connected to one another by polynomials of a higher order, i.e., the points are no longer connected by linear segments, but rather are approximated by curve paths. A disadvantage of this method is that the approximation by polynomials is computationally very intensive, another is that precisely in the case of irregular polylines, undesirably sharp changes in direction can nevertheless occur at the connecting point of two curve paths.